#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
/**
* Problem: Stove (JOI 2017/2018 Final Round)
* Goal: Minimize the total operating time of the stove.
*/
int main() {
// Optimize input and output speed
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int N, K;
if (!(cin >> N >> K)) return 0;
vector<long long> T(N);
for (int i = 0; i < N; ++i) {
cin >> T[i];
}
// Each guest stays for exactly 1 minute (from T_i to T_i + 1).
// If we turn the stove on/off for every guest individually,
// the minimum time is N minutes, using N matches.
long long total_time = N;
// We calculate the gaps between consecutive guests.
// A gap is the time from when guest i leaves (T[i]+1)
// to when guest i+1 arrives (T[i+1]).
vector<long long> gaps;
for (int i = 0; i < N - 1; ++i) {
long long gap_duration = T[i + 1] - (T[i] + 1);
if (gap_duration > 0) {
gaps.push_back(gap_duration);
}
}
// To reduce the number of matches from N down to K,
// we must "fill" (keep the stove on during) N - K gaps.
// To minimize total time, we pick the shortest gaps to fill.
sort(gaps.begin(), gaps.end());
int matches_to_reduce = N - K;
for (int i = 0; i < matches_to_reduce && i < (int)gaps.size(); ++i) {
total_time += gaps[i];
}
cout << total_time << endl;
return 0;
}
